This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-159179 filed Mar. 31, 2000 and No. 2000-118572 filed Apr. 9, 2000, the entire contents of which are incorporated herein by reference.
This invention relates to an ultrasonic probe to be used for ultrasonic diagnosis and ultrasonic flaw detection, a method of manufacturing such a probe and an ultrasonic diagnosis apparatus comprising such a probe.
Conventional ultrasonic probes utilized for ultrasonic diagnosis apparatus comprise a one-dimensional array probe formed by arranging short strip-shaped (narrow box-shaped) piezoelectric vibrators in an array. This is because a technique referred to as an electronic scanning method is generally used for ultrasonic scanning operations for good reasons. With the electronic scanning method, the ultrasonic vibrators of the array are provided with respective delay times when focussing the pulse to be transmitted or the received signal. Since this method allows high speed scanning and high speed alteration of the focal point of the ultrasonic beam to be transmitted or the received ultrasonic beam, it is in the main stream of ultrasonic scanning.
With the above electronic scanning method, in the case of a one-dimensional array probe, the operation of electronic focussing can be conducted on an ultrasonic wave in the direction of arrangement of the piezoelectric vibrators and an ultrasonic beam can be used for scanning. However, only an acoustic lens can be used for focussing in a direction perpendicular to the direction of arrangement (and hence to the surface to be scanned by the ultrasonic wave. This means that it is not possible to dynamically change the focal point. Additionally, any scanning operation using an ultrasonic beam cannot be conducted two-dimensionally (on a plane) because piezoelectric vibrators are arranged only one-dimensionally in conventional ultrasonic probes.
In recent years, efforts have been made to develop systems for three-dimensionally collecting and displaying ultrasonic images by arranging vibrators (ultrasonic vibrators) in the form of a matrix, dynamically focussing the ultrasonic beam in all directions and using the ultrasonic beam for three-dimensional scanning.
For such a system to be realized, it is necessary to use a two-dimensional array ultrasonic probe comprising two-dimensionally arranged vibrators. In other words, the use of a two-dimensional array ultrasonic probe is a prerequisite for realizing omnidirectional focussing and high speed three-dimensional scanning of ultrasonic waves.
Generally, in two-dimensional array probes, vibrators are arranged in the form of a matrix of m rows and n columns. In order to realize three-dimensional dynamic focussing and three-dimensional beam scanning to a satisfactory extent, a number greater than 50 have to be selected for m and also for n and vibrators have to be arranged at a micro-pitch of less than 0.5 mm. Then, more than 2,000 channels of wires have to be led out of an area of about 2 cm square.
Meanwhile, a number of proposals have been made for realizing two-dimensional array probes particularly in terms of process and configuration. For example, Japanese Patent Application KOKAI Publication No. 59-152800 discloses a method of manufacturing a two-dimensional array probe, which will be summarily described below.
Firstly, a grounding plate and a flexible printed circuit board (FPC) are connected respectively to the front and rear surfaces of a raw piezoelectric vibrator and a backing member and an acoustic adjustment layer are formed as in the case of a one-dimensional array probe. Then, the grounding plate and the FPC are bent in an appropriate manner. Subsequently, the vibrator is diced to produce array vibrators and signal leads and grounding wires are led out from the respective lateral sides of the vibrators to produce a one-dimensional array transducer. A two-dimensional array ultrasonic probe is produced by bonding a plurality of such one-dimensional array transducers.
Japanese Patent Application KOKAI Publication No. 2000-138400 discloses an ultrasonic probe comprising layer-built electronic components, including layer-built piezoelectric elements and a flexible printed circuit board bonded to the layer-built piezoelectric elements. In this ultrasonic probe, every other electrode is selected in the layer direction of the piezoelectric elements and the selected electrodes are electrically connected together by means of an electrode pattern of the flexible printed circuit board to form a first group of electrodes, while the remaining electrodes are connected together to form a second group of electrodes. An end of the electrode pattern of the flexible printed circuit board is used as the electrode section for external connection that is also electrically connected to the two groups of electrodes.
Besides the above probes, many other two-dimensional array ultrasonic probes have been proposed and include those obtained by two-dimensionally arranging electrode drawing out terminals in the form of a matrix, drawing out leads therefrom, connecting a piezoelectric vibrator plate onto a substrate and dividing the piezoelectric vibrator plate into matrix in such a way that each vibrator is found on an electrode drawing out terminal.
However, with any of the known methods, it is difficult to realize a two-dimensional array probe comprising a large number of vibrators that are arranged at a micro-pitch with a high productivity and low cost.
Meanwhile, PZT (lead zirconate-titanate) type piezoelectric ceramic materials and lead relaxa-titanate type piezoelectric monocrystalline materials are used as ultrasonic wave receiving materials in the field of medical ultrasonic diagnosis apparatus and non-destructive testing apparatus.
Additionally, as pointed out above, efforts have been made to develop two-dimensional probes comprising two-dimensionally arranged rod-shaped vibrators. By using rod-shaped vibrators, it is possible to use k33 corresponding to the longitudinal vibration of a rod for the vibration mode. The value of k33 is found between 60 and 80% in the case of PZT type ceramic materials and 80 and 94% in the case of relaxa-titanium type monocrystalline materials. These values are promising for realizing high sensitivity probes.
The technology of THI (Tissue Harmonic Imaging) is currently used to capture minute blood flow in the field of ultrasonic diagnosis apparatus. With the technology of THI, higher harmonics of the second degree of the transmitted ultrasonic wave (echo) are received and detected. Therefore, conventional ultrasonic probes realized by adopting the THI technology are forced to use the resonance frequency of the piezoelectric vibrators either for wave transmission or for wave reception or compromise the requirement of transmission and that of reception at the cost of sacrificing the frequency characteristics of the piezoelectric vibrators to a certain extent. As a result, problems arise including an undesired high drive voltage transmitted from the drive circuit and/or a reduced reception sensitivity.
Japanese Patent Application KOKAI Publication No. 11-234797 discloses a technology of using different sets of piezoelectric vibrators for ultrasonic wave transmission and reception. According to the patent document, piezoelectric vibrators are arranged in a single layer as reception vibrators while transmission vibrators are arranged to form a thin multilayer structure to raise the intensity of the transmitted ultrasonic wave. However, any two arrangements of piezoelectric vibrators of the same piezoelectric material formed at the same thickness show a substantially similar center frequency in the operating frequency band. Therefore, the use of the technology of Japanese Patent Application KOKAI Publication No. 11-234797 for THI does not significantly improve the reception sensitivity.
The above problems are particularly serious in two-dimensional array probes because down-sized vibrators are used there to make each vibrator show a reduced transmission/reception capacity.
On the other hand, in conventional two-dimensional array probes, a single piezoelectric vibrator is divided to form a two-dimensional array typically in the manner as described in Japanese Patent Application KOKAI Publication No. 7-170600.
With the technique disclosed in the above patent document, however, newly manufactured ultrasonic probes that mostly contain good vibrators can become faulty if they have even a few defective vibrators, brought about by electrodes peeling off when the single piezoelectric vibrator is cut. Therefore, a high manufacturing yield cannot be expected with the technique.
Japanese Patent Application KOKAI Publication No. 11-234797 discloses technique of uniformly rearranging the produced vibrators with reduced intervals. However, such a rearranging operation requires an extremely high level of precision.
Thus, conventional ultrasonic diagnosis apparatus employing the technology of THI are accompanied by the need of using an undesired high drive voltage transmitted from the drive circuit and/or the problem of a reduced reception sensitivity.
On the other hand, manufacturing two-dimensional arrays requires an extremely high level of precision and hence cannot be expected to provide a high manufacturing efficiency.
In view of the above circumstances, it is therefore an object of the present invention to provide a two-dimensional array ultrasonic probe that can be manufactured easily and efficiently and operates with a high sensitivity and low inter-vibrator cross talk, a method of manufacturing such a probe and an ultrasonic diagnosis apparatus comprising such a probe.
Another object of the present invention is to provide an ultrasonic probe adapted to THI technology that can suitably be used for ultrasonic diagnostic operations using THI technology to realize low power consumption and high sensitivity, a method of manufacturing such an ultrasonic probe in a simple way and an ultrasonic diagnosis apparatus comprising such a probe.
In a first aspect of the invention, the above objects are achieved by providing an ultrasonic probe comprising a plurality of piezoelectric vibrators, a plurality of substrates having a plurality of signal lines on one of the surfaces thereof, the plurality of piezoelectric vibrators being arranged to form an array and one of the vibrator connected respectively to one of the signal lines, the plurality of substrates being arranged at predetermined intervals so that the plurality of piezoelectric vibrators is arranged in matrix arrangement, and a holding means for rigidly holding the plurality of substrates.
Thus in the first aspect of the invention, it is possible to provide a two-dimensional ultrasonic probe wherein printed circuit boards are arranged in the respective gaps separating the two-dimensionally arranged piezoelectric vibrators so as to draw electric wires therefrom for connection with the signal electrodes and the electrode connectors at lateral sides of the vibrators are connected respectively to the corresponding electric connectors on the printed circuit boards so that the signal lines from the signal electrodes of the piezoelectric vibrators can be taken out on a column by column basis.
In a second aspect of the present invention, there is provided an ultrasonic probe comprising a plurality of first vibrators adapted to transmit a first ultrasonic wave in a first frequency band to an object of examination and a plurality of second vibrators adapted to receive the reflected waves from the object of examination produced on the basis of the first ultrasonic wave in a second frequency band, the plurality of first vibrators and the plurality of second vibrators being arranged in the form of a matrix to produce an ultrasonic wave irradiation surface, the center frequency of the second frequency band being higher than the center frequency of the first frequency band.
Differently stated, two groups of vibrators with different resonance frequencies are used respectively as vibrators for transmitting an ultrasonic wave and those for receiving an ultrasonic wave in an ultrasonic probe. With this arrangement, an ultrasonic wave having a frequency different from that of the transmitted ultrasonic wave can be detected with a high sensitivity.
Generally, with THI technology adapted to receive the higher harmonics of the second degree of echo of an ultrasonic wave, it is desirable that the resonance frequency of the wave receiving vibrators is higher than that of the wave transmitting vibrators. To be more specific, the resonance frequency of the wave receiving vibrators is higher than that of the wave transmitting vibrators preferably by 1.5 to 3 times, more preferably by about two times.
Therefore, in the second aspect of the invention, an ultrasonic probe according to the invention can show an improved sensitivity for receiving an ultrasonic wave and a reduced drive voltage for transmitting an ultrasonic wave.
In a third aspect of the invention, there is provided an ultrasonic diagnosis apparatus comprising an ultrasonic probe having a plurality of first vibrators adapted to transmit a first ultrasonic wave in a first frequency band to an object of examination and a plurality of second vibrators adapted to receive the reflected waves from the object of examination produced on the basis of the first ultrasonic wave in a second frequency band, a drive circuit for driving the first vibrators with a signal having a predetermined frequency and a detection circuit for detecting the reception signal received by the second vibrators and taking out the higher harmonics of the second degree of the signal having the predetermined frequency.
Thus, an ultrasonic diagnosis apparatus in accordance with the third aspect of the invention can show an enhanced level of reception sensitivity and operates with a reduced drive voltage for transmitting an ultrasonic wave.
In a fourth aspect of the invention, there is provided an ultrasonic diagnosis apparatus comprising an ultrasonic probe having a plurality of piezoelectric vibrators including a plurality of first vibrators adapted to transmit a first ultrasonic wave in a first frequency band to an object of examination and a plurality of second vibrators adapted to receive the reflected waves from the object of examination produced on the basis of the first ultrasonic wave in a second frequency band, a plurality of substrates carrying a plurality of signal lines on one of the opposite surfaces thereof, the plurality of piezoelectric vibrators being arranged to form a matrix and connected respectively to the signal lines on a one to one basis, the plurality of substrates being arranged at predetermined intervals so as to adapt themselves to the matrix arrangement of the plurality of piezoelectric vibrators, and a securing means for rigidly securing the plurality of substrates, a drive circuit for driving the first vibrators with a signal having a predetermined frequency and a detection circuit for detecting the reception signal received by the second vibrators and taking out the higher harmonics of the second degree of the signal having the predetermined frequency.
Thus, an ultrasonic diagnosis apparatus in accordance with the fourth aspect of the invention can show an enhanced level of reception sensitivity and operates with a reduced drive voltage for transmitting an ultrasonic wave.
In a fifth aspect of the invention, there is provided a method of manufacturing an ultrasonic probe comprising a step of electrically connecting the electrodes of a plurality of layer-built piezoelectric vibrators respectively to corresponding signal lines arranged at a predetermined pitch on one of the surfaces of a plurality of substrates and mounting the layer-built piezoelectric vibrators with the lateral surfaces thereof held in contact with the respective substrates and a step of forming an ultrasonic wave transmitting surface carrying thereon the layer-built vibrators arranged two-dimensionally by arranging the plurality of substrate with the plurality of layer-built vibrators mounted thereon.
With the method of manufacturing an ultrasonic probe in accordance with the fifth aspect of the invention, it is now possible to manufacture an ultrasonic probe with a high sensitivity and low inter-vibrator cross talk relatively easily in order to realize a high manufacturing efficiency.
Additional objects and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention.
The objects and advantages of the present invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.